Modular lattice signatures, revisited

In this paper we revisit the modular lattice signature scheme and its efficient instantiation known as pqNTRUSign. First, we show that a modular lattice signature scheme can be based on a standard lattice problem. The fundamental problem that needs to be solved by the signer or a potential forger is recovering a lattice vector with a restricted norm, given the least significant bits. We show that this problem is equivalent to the short integer solution (SIS) problem over the corresponding lattice. In addition, we show that by replacing the uniform sampling in pqNTRUSign with a bimodal Gaussian sampling, we can further reduce the size of a signature. An important new contribution, enabled by this Gaussian sampling version of pqNTRUSign, is that we can now perform batch verification of messages signed by the same public key, which allows the verifier to check approximately 24 signatures in a single verification process.